RHBA-2012:1254 - Bug Fix Advisory

Topic

Updated kernel packages that fix three bugs and add two enhancements are now
available for Red Hat Enterprise Linux 6 Extended Update Support.

Description

The kernel packages contain the Linux kernel, the core of any Linux operating
system.

This update fixes the following bugs:

• Previously, the TCP socket bound to NFS server contained a stale skb_hints

socket buffer. Consequently, kernel could terminate unexpectedly. A patch has
been provided to address this issue and skb_hints is now properly cleared from
the socket, thus preventing this bug. (BZ#846831)

• On Intel systems with Pause Loop Exiting (PLE), or AMD systems with Pause

Filtering (PF), it was possible for larger multi-CPU KVM guests to experience
slowdowns and soft lock-ups. Due to a boundary condition in kvm_vcpu_on_spin,
all the VCPUs could try to yield to VCPU0, causing contention on the run queue
lock of the physical CPU where the guest's VCPU0 is running. This update
eliminates the boundary condition in kvm_vcpu_on_spin. (BZ#847041)

• Due to a missing return statement, the nfs_attr_use_mounted_on_file() function

returned a wrong value. As a consequence, redundant ESTALE errors could
potentially be returned. This update adds the proper return statement to
nfs_attr_use_mounted_on_file(), thus preventing this bug. (BZ#847944)

This update adds the following enhancements:

• This update adds support for the Proportional Rate Reduction (PRR) algorithms

for the TCP protocol. This algorithm determines TCP's sending rate in fast
recovery. PRR avoids excessive window reductions and improves accuracy of the
amount of data sent during loss recovery. In addition, a number of other
enhancements and bug fixes for TCP are part of this update. (BZ#847732)

• This update affects performance of the O_DSYNC flag on the GFS2 file system

when only data (and not metadata such as file size) has been dirtied as a result
of the write() system call. Prior to this update, write calls with O_DSYNC were
behaving the same way as with O_SYNC at all times. With this update, O_DSYNC
write calls only write back data if the inode's metadata is not dirty. This
results in a considerable performance improvement for this specific case. Note
that the issue does not affect data integrity. The same issue also applies to
the pairing of the write() and fdatasync() system calls. (BZ#849550)

All users are advised to upgrade to these updated packages, which fix these bugs
and add these enhancements. The system must be rebooted for this update to take
effect.

Solution

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/knowledge/articles/11258

Affected Products

• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.2 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.2 i386
• Red Hat Enterprise Linux Server - AUS 6.2 x86_64
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.2 s390x
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.2 ppc64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.2 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.2 i386
• Red Hat Storage 2.0 x86_64
• Red Hat Gluster Storage Server for On-premise 2.0 x86_64
• Red Hat Storage for Public Cloud (via RHUI) 2.0 x86_64

Fixes

• BZ - 847944 - nfs_attr_use_mounted_on_file() returns wrong value [rhel-6.2.z]

CVEs

(none)

References

(none)